Editing affect (emotion) in speech has many desirable applications. Editing tools have become standard in computer graphics and vision, but speech technologies still lack simple transformations to manipulate expression of natural and synthesized speech. Such editing tools are relevant for the movie and games industries, for feedback and therapeutic applications, and more. There is a substantial body of work in affective speech synthesis, see for example the review by Schröder M. (Emotional speech synthesis: A review. In Proceedings of Eurospeech 2001, pages 561-564, Aalborg). Morphing of affect in speech, meaning regenerating a signal by interpolation of auditory features between two samples, was presented by Kawahara H. and Matsui H. (Auditory Morphing Based on an Elastic Perceptual Distance Metric, in an Interference-Free Time-Frequency Representation, ICASSP'2003, pp. 256-259, 2003). This work explored transitions between two utterances with different expressions in the time-frequency domain. Further results on morphing speech for voice changes in singing were presented by Pfitzinger (Auditory Morphing Based on an Elastic Perceptual Distance Metric, in an Interference-Free Time-Frequency Representation, ICASSP'2003, pp. 256-259, 2003), who also reviews other morphing related work and techniques.
However most of the studies explored just a few extreme expressions, and not nuances or subtle expressions. The methods that use prosody characteristics consider global definitions, and only a few integrate the linguistic prosody categorizations such as ƒ0 contours (Burkhardt F., Sendlmeier W. F.: Verification of Acoustical Correlates of Emotional Speech using Formant-Synthesis, ISCA Workshop on Speech \& Emotion, Northern Ireland 2000, p. 151-156; Mozziconacci S. J. L., Hermes, D. J.: Role of intonation patterns in conveying emotion in speech, ICPhS 1999, p. 2001-2004). The morphing examples are of very short utterances (one short word each), and a few extreme acted expressions. None of these techniques leads to editing tools for general use.